Communication systems are known to include at least one console and a plurality of communication units, such as hand-held portable or vehicle-mounted mobile radios, organized into multiple communication talkgroups. A communication talkgroup is a set of logically united communication units capable of engaging in group-wide communications. A console is a fixed-end device that allows a dispatcher, operating at a central location, to communicate with individual communication units and/or entire talkgroups. Furthermore, a console can typically monitor communications occurring amongst multiple talkgroups. That is to say, audio derived from multiple talkgroup communications is summed and routed within the console so that an operator of the console can monitor the communications. The use, however, of digital voice compression schemes within communication systems renders the implementation of console monitoring more difficult.
Unlike analog voice or digital PCM (pulse-code modulation) voice, digitally-compressed voice, such as VSELP (vector-sum excited linear predictive coding), is not directly summable. In order to sum multiple compressed voice signals, it is necessary to first convert the compressed signals into a summable format, such as PCM. In a communication system utilizing digitally-compressed voice and containing a large number of talkgroups, a similarly large number of converters, dedicated to individual talkgroups, would be required in order to provide monitoring capability within a console. Unfortunately, the design complexity and cost of providing a large number of converters within a console are prohibitive. Therefore a need exists for a method that allows multiple, digitally-compressed talkgroup communications to be efficiently monitored by a console.